It has been reported that 1-.beta.-D-arabinofuranosyl-(E)-5-(2-halogenovinyl)uracil (XVAU) was synthesized first by Sakata and Machida and that a compound of this type possesses an extremely potent antiviral activity (see Japanese Patent Publication No. 48160/1982 and U.S. Pat. No. 4,386,076).
It is generally considered that one of the conditions required for a compound having an antiviral activity to be an excellent antiviral agent is that its concentration in blood can be kept high for many hours when it is administered orally.
Although it can be said that the above-described XVAU is a compound having a potent antiviral activity, the sustention of XVAU in blood when it is orally administered is still unsatisfactory when the above condition is taken into consideration.
An object of the present invention is therefore to provide novel XVAU derivatives which can increase the concentration of XVAU in blood and can keep it high for many hours when the derivatives are orally administered. If this object is attained, it would be expected that a treatment can be carried out efficiently with less amount of a medicine and/or fewer times of administration of the medicine.